Types of in vitro fertilisation (IVF)

Many couples are able to conceive and establish a healthy pregnancy by having infertility treatment. One of the most used methods is in vitro fertilisation, which was first performed successfully in 1978. The overall process of in vitro fertilisation is described in this guide; this article outlines the different variations in IVF that have been developed over the last 30 years and that are offered by fertility clinics around the world.

Natural cycle in vitro fertilisation

This variation on in vitro fertilisation does not involve stimulating the woman’s ovaries to produce several eggs for collection. Just the one egg produced as part of her normal menstrual cycle is collected and then combined with her partner’s sperm to achieve fertilisation and, hopefully, a viable embryo.

This method of in vitro fertilisation has the advantages that it does not carry the risk of ovarian hyperstimulation, and it is also more acceptable to some cultures and religious groups as no spare embryos are created, which may then need to be disposed of or frozen. It also has the same risk of multiple pregnancy as natural conception.

On the downside, the success rates for natural cycle in vitro fertilisation are not that high. To be fair, the statistics are not readily available as so few procedures of this type are performed. As an example, figures published by the UK’s Human Fertilisation and Embryology Authority (HFEA) show that only one woman of the 26 aged under 35 became pregnant in 2008 as a result of natural cycle in vitro fertilisation.

Mild stimulation in vitro fertilisation

This procedure is performed in exactly the same way as standard in vitro fertilisation except that the hormones used to stimulate the ovaries to produce several eggs are used at a lower dose or for a shorter time. This can reduce the risk of ovarian hyperstimulation syndrome in women who have developed this in previous in vitro fertilisation cycles, and in women who have polycystic ovary syndrome (PCOS).

Mild stimulation may also omit the initial treatment to suppress your own menstrual cycle, which means you may not find this phase of treatment as uncomfortable, as no menopausal-like symptoms will be apparent.

Disadvantages of this form of in vitro fertilisation are reduced numbers of eggs available for collection, and so potentially fewer embryos to choose from for transfer. However, because the ovaries are not stimulated in the same way, you do not have to wait so long to repeat a cycle of in vitro fertilisation. You can have three to four cycles within six months, as long as they all involve only mild stimulation.

Data published in The Lancet have shown that after one year of trying for a baby with mild stimulation IVF, 43.4 % of women became pregnant compared with 44.7 % having standard in vitro fertilisation, which is hardly any difference. The comparable results, combined with the significant difference in cost (mild stimulation in vitro fertilisation is cheaper), mean that this is becoming an infertility treatment worthy of more consideration.

Types of embryo transfer after in vitro fertilisation

Whatever the type of preparation you have for IVF, the fertilisation process is generally the same in all methods. There are then different options, depending on whether you have embryos transferred at 2–3 days old or 5–6 days old, and whether you have embryo transfer done immediately or the embryos are frozen and transferred at a future date.

These variations are summarised here, and you can find more detailed information in other articles in this guide by following the relevant links:

Fresh embryo transfer: after in vitro fertilisation, any fertilised eggs are cultured for a further 1–2 days and the highest quality embryos are chosen for transfer. For a woman under 40, the UK’s HFEA recommends two embryos be transferred, for women over 40, three embryos can be used. Other countries do not have such strict rules; the case of the octuplets born after a doctor in the USA transferred 12 embryos caused great controversy in 2009; rules may be tightened in the future.

Fresh blastocyst embryo transfer: if several healthy embryos develop after in vitro fertilisation, the medical team may recommend waiting another couple of days to see if any develop into blastocysts. Blastocyst embryo transfer has a higher success rate than 2–3 day embryo transfer.

Frozen embryo or blastocyst transfer (FET): spare healthy embryos or blastocysts not used for transfer in the first in vitro fertilisation cycle can be frozen and stored for future use. This can be done to avoid having to stimulate the woman’s ovaries for a repeat IVF cycle following treatment failure, or to try for another child a couple of years later. Frozen embryo transfer is also useful if the woman has had standard in vitro fertilisation, with high levels of stimulation of her ovaries, and has developed ovarian hyperstimulation syndrome. The frozen embryos or blastocysts can be transferred once her body has recovered.

Assisted hatching (AH): although there is not enough evidence to say that this technique definitely increases success rates of in vitro fertilisation, some women do benefit from having their embryos treated to weaken the outer layer before being transferred into the uterus. Many fertility clinics around the world will recommend assisted hatching under specific circumstances, if you have had several failed cycles of in vitro fertilisation, for example.